Movement pile
A moving cluster or moving star cluster is a loose group of stars that are not characterized by a spatial concentration around a cluster center, but by a common direction of movement towards a distant convergence or vanishing point (see also apex ).
The stars of a moving cluster have a common origin in an open star cluster which, due to the low gravitational bond, dissolves after a few orbits around the galactic center ; the transition to the type of open star clusters or star association is fluid. A second hypothesis explains the formation of motion clusters through an orbital resonance with the spiral structure of the Milky Way .
If a movement cluster is very close to the solar system - such as the bear stream with 5 bright stars in the Big Dipper - you cannot directly recognize it as coherent, but only on the basis of the proper movements of its individual stars .
Well-known examples of movement clusters , the belonging together of which is directly recognizable due to their great distance , are the Hyades in Taurus and the crib ( Praesepe ) in Cancer. The Pleiades, on the other hand, belong to the open star clusters because of their star concentration.
See also
literature
- F. Liu et al .: Chemical composition of giants from two moving groups . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1203.1452v1 (English).